An examination of existing legacy land line communications networks in light of communications technology evolution leads to some interesting insights. On the one hand, the newest long haul communications and information infrastructures being built today are based on fiber optic and coding technologies which are capable of immense capacity. On the other hand, the "last mile" local drop to the end user is typically still the legacy copper line installed decades ago for telephone service. Because the legacy copper lines were designed for performance that did not contemplate today's fiber optic capabilities, the copper line end users cannot avail themselves of the high bit rates that modem long haul infrastructure can provide. The user is limited by his local drop connection to the service provider.
Looking at the communications system architectures currently being pursued by service providers, nearly all suffer from implicit assumptions that preserve the notion of connection based service. Both of these background aspects are discussed below.
The "Last Mile"
The use of telecommunication resources has moved well beyond mere telephone calls. These voice communications messages are no longer the dominant kind of information flowing through the world's communication networks. Telecommunication users today utilize these resources for many other forms of information. Computer data and video are just examples of the future. Users are requiring that their communication link to the global networks rise to the occasion in terms of bandwidth, that is, digital data rate capability. The legacy links as well as the architecture of the central office (telephone exchange) and its cable to the user cannot deliver the information capability desired for all this data, video and other information.
There is a need for new network architecture that provides a broad bandwidth path to the user which can fulfill both present and future requirements. For any such new cable system, suitable bandwidth should be provided for today's end user with an electrical signal interface--not optical--while at little additional cost allowing the capability for optical signal transfer for that time when both the equipment and the end user's bandwidth utilization needs evolve. For the present, and the near future, the largest user bandwidth generally required (even for two-way communications) may still be contained within an interface providing a total channel capacity of under one Gigabit per second. Relatively short spans are required to connect from any local distribution nodes of a new network. Certainly most such cable runs are well under the mile distance of the "Last Mile" appellation that has been applied to this class of cable system, and most of those runs (or local drops) will be well under a half mile. Such new networks' distribution "backbone" linking nodes may be well served by two-way fiber optic channels connecting many nodes envisioned for such a regional network. With the advent of digital signal transmission technology, the performance requirements for these local drops, or "last mile" legs of the cable system, present new and quite different objectives than have been addressed by the prior art. It is also possible that with an insightful electrical design, such a last mile cable may even be suitable for some short-haul inter-node links.
The cost of installing any cable system to individual users--not the cable itself--is substantial and is by far the largest portion of the network investment required of service providers. It is highly desirable if not essential that any new installation of such drop cables provide for future growth in capacity.
A Paradigm Shift in Network Architecture
Past communication networks have been almost entirely based on a "call" or "message" type of traffic where users were connected only transiently to the network while "calling" or being "called." Such connection based architecture established a temporary connecting path between caller and receiver. In the future, communications will be based on the "packet" switching principle. A packet message carries address information so that the sender gets the message to the receiver and vice-versa. All users may be continuously connected to such a new network. Users will elect to actively participate and produce information "messages" only when they wish. The majority of activity in such a network will exist with data flowing, if only intermittently yet with great frequency to and from the user in a fashion not requiring the presence or active participation of the user. This kind of function more resembles the supply of electric power to users than the present call or connection based communication function except that such messages also originate from the user's installation as well as coming to the user from diverse sources foreign to the user's location. This represents new uses of communication processes to accommodate such functions as exemplified by network "agents" or "avatars" which operate independently delivering information whenever their function requires. Similarly the user's system may originate information as a result of similar programming. "Passive" (i.e., non-user attention demanding) functions may in the very near future become the dominant volume of information traffic to be carried by the network.
Such a future requires significant increases in data rates. For example, in 1997, the entire volume of information flow in all long lines occurred with a rate of something just under 1.times.10.sup.14 bits per second. It is likely that in just a few years one billion users may be connected by networks at which time the global information rate may approach 1.times.10.sup.19 to 1.times.10.sup.20 bits per second!
Although much of the fiber now in place in the world is dark, data rate growth will eventually present challenges. The use of wavelength division multiplexing ("WDM") in the optical carriers employed for fiber, as well as optical amplifiers and dispersion correction, can increase their capacity by several hundred times. Even so, large amounts of new fiber will be required to support ever larger and more ambitious applications. This will simply further aggravate the need for substantial bandwidth at the user's end of network systems. Improvements to meet this need must deliver hundreds of Megabits per second, in send and receive modes, and preferably in duplex, i.e., simultaneously sending and receiving.
Many needs, unique to the last mile cable system, significantly affect the feasibility of last mile designs and influence its cost, durability and reliability. Present communication systems are capable of providing only limited bandwidth to the user even though their backbones in long distance and most local inter-exchange paths are fiber based systems. Existing fiber paths have generally utilized only a very small portion of the information bandwidth potential of such fiber paths. The technology of 1997, for example, as mentioned above, provides the opportunity of sending many signals over a single fiber and of having each of those signals carry 10 to 20 Gigabits per second.
The optical fiber is presently in place; only the "terminal" connection is required to achieve such a result. Presently, some "Common Carriers" have been installing such bandwidth enhancing means on their networks' long haul portions just to handle their current and projected loads. There still exists considerable bandwidth capacity latent in those paths; however, little or no feasible technology presently exists to deliver substantial two-way bandwidth at the user terminal end of existing communication networks. Further significant is the current status of fiber use: most of the fibers now installed are dark. That is, they are in place but carry no signals. Present bandwidth limitations lie simply in the means to deliver the existing and the latent long haul bandwidth locally to the entire public at the same time.